Ball and dual socket joint

ABSTRACT

A spinal implant is inserted between adjacent vertebrae to function as an disk prosthesis. The prosthesis has two plates fastened to adjacent vertebrae facing each other. The facing sides of the plates each have a depending skirt formed as concentric arcs of about 90 degrees. The skirts are either bowed or tapered in the axial direction. Depressions are centrally located between the arcs of the plates and a ball is universally movable in the depressions. A spring mechanism is centrally located in the plates to provide axial compression. The plates are oriented to each other with the concentric arcs of each interrupted skirt at 90 degrees and the protrusion is engaged in the depression. The plates are then rotated about 90 degrees and the opposed arcs of one plate interlock with the opposed arcs of the other plate to prevent separation in the axial direction.

RELATED APPLICATIONS

This application is a continuation-in-part of a U.S. patent applicationSer. No. 11/025,656, entitled Ball-In-Cage Spinal Implant, filed Dec.28, 2004 now abandoned which is related to U.S. application Ser. No.10/793,433, filed Mar. 3, 2004 which is a continuation-in-part of U.S.application Ser. No. 10/792,399, filed Mar. 2, 2004.

FIELD OF THE INVENTION

This invention relates to orthopedic surgery and, in particular, spinalimplants for replacement of ruptured or excised spinal disks.

BACKGROUND OF THE INVENTION

Several attempts have been made to design a spinal prosthesis forreplacement of missing or excised disk material that replicates thefunctions of the missing tissue. U.S. Pat. No. 4,759,769 to Hedman et aldiscloses an artificial disk device in which two plates are attached tothe adjacent vertebrae by bone screws inserted through flanges on theplates. A spring biasing mechanism is captured between the plates tosimulate the actions of the natural disk material. U.S. Pat. No.5,246,458 to Graham and U.S. Pat. No. 6,228,118 to Gordon disclose otherintervertebral implants with arcuate flanges used to connect the deviceto adjacent vertebra. Graham also teaches a resilient structure.

The patents to Marnay, U.S. Pat. No. 5,314,477, Buttner-Janz et al, U.S.Pat. No. 5,401,269, Yuan et al, U.S. Pat. No. 5,676,701, and Shelokov,U.S. Pat. No. 6,039,763, all are directed to the design of the opposingfaces of the adjacent plates of an implant to provide a limiteduniversal joint to simulate the natural movement of the spine.

U.S. Pat. No. 5,683,465 to Shinn et al teaches two plates with bowshaped skirts which are interlocked.

SUMMARY OF THE PRESENT INVENTION

The invention is directed to a spinal implant for insertion betweenadjacent vertebrae to function as an disk prosthesis. The prosthesis isformed from two plates fastened to adjacent vertebrae facing each other.The facing sides of the plates each have a depending skirt formed asconcentric arcs of about 90 degrees. The skirts are either bowed ortapered in the axial direction. A depression is centrally locatedbetween the arcs of both plates. A spring mechanism is centrally locatedon one or both of the plates to provide axial compression. A sphere orball is placed in the central depression of one of the plates. Theplates are oriented to each other with the concentric arcs of eachinterrupted skirt at 90 degrees and the ball is engaged in thedepression of the other plate. The plates are then rotated about 90degrees and the opposed arcs of one plate interlock with the opposedarcs of the other plate to prevent separation in the axial direction.

Therefore, it is an objective of this invention to provide a spinalimplant for axial support of the spinal column which replicates thedimensions and function of an intervertebral disk.

It is another objective of this invention to provide a kit including allthe components for assembly and surgical placement of an artificialspinal disk.

It is a further objective of this invention to provide a method ofassembly of the components of the kit which results in an axiallyinterlocked spinal implant.

It is yet another objective of this invention to provide a ball andsocket joint between two plates attached to adjacent vertebraepermitting axial rotation, lateral bending, vertical tilting and axialcompression.

It is a still further objective of this invention to provide shapedinterrupted skirts on two plates which act as stop limits for tiltingand bending.

It is another objective of this invention to provide an axiallyresilient ball and socket joint.

It is a further objective of this invention to provide a polymericmaterial between the two plates for replicating the function of thenatural disk and preventing boney ingrowth.

Other objectives and advantages of this invention will become apparentfrom the following description taken in conjunction with theaccompanying drawings wherein are set forth, by way of illustration andexample, certain embodiments of this invention. The drawings constitutea part of this specification and include exemplary embodiments of thepresent invention and illustrate various objects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective of the disassembled cage of thisinvention;

FIG. 2 is an exploded perspective of a disassembled plate of the spinalimplant of FIG. 1;

FIG. 3 is a cross section of the assembled implant of this invention;

FIG. 4 is a cross section of another embodiment of the assembled implantof this invention;

FIG. 5 is a perspective of the embodiment shown in FIG. 4;

FIG. 6 is a cross section of another embodiment of the assembled implantof this invention;

FIG. 7 is a perspective of the assembled implant of this inventionshowing a bone attachment device; and

FIG. 8 is a perspective of the assembled implant of this inventionshowing another bone attachment device.

DETAILED DESCRIPTION OF THE INVENTION

The spinal implant 10, shown in FIG. 1, has three major components, anupper plate 11, a lower plate 12 and a universally rotatable sphere orball 50. The upper plate 11 and the lower plate 12 form a cage whenassembled with the ball 50 captured for universal movement within theinterior of the cage. Of course, the position of the plates can bereversed, in use. Both upper plate 11 and lower plate 12 have a planform substantially the size and shape of the end wall of the vertebrabetween which the implant will be placed to produce the maximum area ofcontact between the implant and the vertebra for stability and support.Obviously, different sized plates are necessary because of thedifference in size of vertebra within regions of the spinal column andthe different sizes or ages of patients.

The upper plate 11 has a planar surface 14 for contact with the end wallof a vertebra and an opposite disk surface 15. Depending from the disksurface is an interrupted skirt 16 with opposed arcs 17 and 18. The arcsare approximately 180 degrees apart at their centers and extend about 90degrees. The diameter of the arcs is less than the periphery of theplate 11 leaving a horizontal flange 19. Centrally located within thesemi-circular arcs is a through bore 13. A sleeve 51 is inserted in thethrough bore 13 and telescopes in the plate 11. The sleeve 51 has aspherical depression 52 facing plate 12.

The lower plate 12 has a planar surface 20 for contact with the end wallof a vertebra and an opposite disk surface 21. Upstanding from the disksurface is an interrupted skirt 22 with opposed arcs 23 and 24. The arcsare approximately 180 degrees apart at their centers and extend about 90degrees. The diameter of the arcs is less than the periphery of theplate 12 leaving a horizontal flange 25. Centrally located within thesemi-circular arcs is a through bore 26. A sleeve 53 is inserted in thethrough bore and reciprocates in the plate 12. The sleeve 53 has adepression 54 that is rounded and shaped to closely mirror the contoursof the depression 52. The depressions 52 and 54, as well as the diameterof the ball 50, are of such dimensions as to support the weight of thespinal column.

As shown, though the relationship could be reversed, the opposed arcs 17and 18 of the depending interrupted skirt 16 are concentric with theopposed arcs 23 and 24 of the upstanding interrupted skirt and of lesserdiameter allowing rotation of the plates relative to each other withsurface contact between the outer surface 28 of the depending arcs andthe inner surface 29 of the upstanding arcs.

The spinal implant provides support and range of motion similar to thenatural joint in that the plates 11 and 12 may rotate axially limited bynatural anatomical structures, such as tendons, ligaments and muscles.To simulate the compression of the natural disk during normalactivities, such as walking, a spring mechanism 60, 61 is placed in thevertical axis of the plates 11 and 12. The springs are resilientlycompressionable.

The spring retainer 63 is in the opposite end of sleeve 51 from thedepression 52. The annular spring retainer 63 is formed by theupstanding end wall of the sleeve and the dome shaped central portion.An O-ring spring 60 is disposed in the spring retainer 63. The spring 60and the sleeve 51 are held in the plate 11 by dome cover plate 56.

The sleeve 53 is resiliently supported on the spring 61 in the form of aresilient O-ring. The spring is held in the cavity 64 by the dome coverplate 55. Each of the dome cover plates has a laser weld 57, 58 or otherbond to their respective plates. By absorbing some of the longitudinalloads, the prosthesis lessens the stresses on the adjacent naturaldisks. Further, during placement of the prosthesis, the springs may becompressed to lessen the overall height of the prosthesis.

To further imitate the function of a natural disk, the plates 11 and 12may have a resilient material inserted therebetween, as shown in FIGS.4, 5, and 6. The plates may be connected by a flexible or elastomericmembrane 70, as shown in FIG. 4. The membrane 70 can be discontinuousand, act as a plurality of elastic bands about the periphery of theplates 11 and 12. Or the membrane 70 may be a continuous annular wallattached to the opposite flanges 19 and 25. A viscous polymeric compound71 may occupy the space between the plates, such as a high molecularweight polyethylene or silicone. The membrane may be in the form of anouter skin integral with the polymeric compound. The viscosity of thematerial may vary from that of a gel to that of a solid. The polymericcompound may be molded or otherwise sealed between the plates 11 and 12.The continuous membrane discourages boney ingrowth which can limitspinal movement. As the neck is turned or tilted, the insert will becompressed on one side and extended on the other side producing acushioning effect and a tendency to return to a state of equilibrium.

As shown in FIG. 6, an elastomeric plug 72 may be inserted between theplates and attached to one or both the plates 11 and 12. The plug 72operates in the same manner as the polymeric compound discussed above.

The spine may bend laterally and tilt medially in flexion/extension in arange comparable to the normal range of motion. The inserts 71 and 72may also having varying viscosities or moments of elasticity tailored tothe area of the spine in which they are to be implanted.

The implant also provides limitation of these movements throughinteraction of the depending arcs and the upstanding arcs. As shown inFIG. 3, the components of the implant are connected together byorienting the interrupted skirts 16 and 22 at 90 degrees to each other.This action overlaps the interrupted skirts vertically. The plates arerotated through 90 degrees relative to each other. This rotation alignsthe depending opposed arcs with the upstanding opposed arcs andinterlocks the plates in a movable joint that cannot be separatedaxially. The inner surface 28 of the interrupted skirt 16 slidablycontacts the outer surface 29 of the interrupted skirt 22. Thecontacting surfaces are spherical or bowed, from the plate at least tothe height of the diameter of the ball 50, forming another ball andsocket joint with the bottom edge of the depending arc 23 of a largerdiameter than the top edge of the upstanding arc 17 by which the platesare interlocked. Of course, the remainder of the inner and outersurfaces of the interrupted skirts may be straight or tapered and spacedapart to allow for bending and tilting. In this instance, thecooperating interrupted skirts act as an bending stop when they come incontact with the opposite plate.

FIG. 4 also illustrates a modification of the dynamic spring action ofthe implant of FIG. 2. The depression 52 is formed on a slidable sleeve51 in a bore 13 of the plate. The sleeve 51 is solidly mounted in thebore 13. The sleeve 51 may be formed integrally with the dome coverplate as a one piece component, in which case, the plug is then laserwelded or otherwise bonded into the plate 11. Plate 12 may be formed inthe same fashion. This embodiment is less complex and less expensive tofabricate. It does not have the dynamic characteristics of the implantcontaining the O-ring.

In FIG. 7, a fastener is shown in the form of spikes 34 attached orformed on flanges 19 and 25 which are to be driven into the end walls ofthe adjacent vertebra. As shown in FIG. 8, each of flanges 19 and 25 ofthe spinal implant has a vertical extension with apertures 32, 33 whichcooperate with bone screws to mount the spinal implant on the vertebra.As shown, the vertical extensions are disposed in line with each other.However, the vertical extensions can be on opposite lateral sides of theflanges 19 and 25 permitting fastening of each plate on the oppositeside of adjacent vertebrae. Of course, the two fasteners may be usedtogether, eg., the spikes may be on one plate and the verticalextensions on the other plate of the same spinal implant.

The components are made from materials that are suitable forimplantation in the living body and have the requisite strength toperform the described functions without deformation, e.g., the opposedbearing surfaces of the depressions and ball may be made of metal or aceramic and a metal, respectively, the ceramic material is implant gradealumina ceramic or a silicon nitride or carbide and the metal may be anitrogen alloyed chromium stainless steel or cobalt chrome alloy, ortitanium, and alloys of each, coated metals, ceramics, ceramic coatings,and polymer coatings.

The plates may be made entirely of cobalt chrome alloy or only theinserts. In the high wear areas, such as the depressions coatings orinserts may be used to prevent galling and permit repair. In thismodular concept, the end plates may be titanium, titanium alloy, orstainless steel among other materails as discussed above.

The prosthetic ball 50 is preferably made from an implant grade aluminaceramic or a silicon nitride or silicon carbide material. The ball 50may be formed entirely of the ceramic material or a ceramic coating onanother matrix. The alumina ceramic or silicon nitride or siliconcarbide material can be hot isostatic pressed (HIPing). The ball 50 isthen polished to a mirror-like finish. The ceramic ball is completelycorrosion resistant and is non-abrasive. The solid matrix eliminates thewear particles, such as liberated from metal, other coated metals andpolyethylene implants. The ball 50 has excellent thermal conductivitythereby reducing patient discomfort associated with exposure to coldweather. Further, the alumina ceramic or silicon nitride implant willreact well with x-ray and MRI (magnetic resonance imaging) diagnosticprocedures.

The kit contains plates with protrusions and skirts of varying lengthsto allow selection of components for an implant with the axial dimensionsubstantially the same as the thickness of the disk the implant willreplace. The kit may also contain upper and lower plate components ofvarying sizes. A prosthesis could be assembled from the kit with springsin the upper and lower plates.

A number of embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiment but only by the scope ofthe appended claims.

1. A spinal implant for placement between adjacent vertebrae to replacedisk material comprising a first plate and a second plate adapted tointerlock about a central axis, said first plate having a planarvertebrae engaging side and a disk side, a first interrupted skirt onsaid disk side extending approximately normal to said plate, said skirtformed as opposing separated arcs, a depression along said central axisof said disk side of said plate centrally located between said opposingarcs, said second plate having a second planar vertebrae engaging sideand a second disk side, a second interrupted skirt on said second diskside extending approximately normal to said second plate, said secondskirt formed as opposing separated arcs, a second depression along saidcentral axis of said second disk side of said second plate centrallylocated between said opposing arcs and a universally rotatable ballcaptured in said depressions whereby said first plate is adapted tocontact a vertebrae and said second plate is adapted to contact anadjacent vertebrae with said depressions each adapted to form a bearingsurface for said ball along said central axis and said first and secondinterrupted skirts are interlocked forming a universal joint.
 2. Thespinal implant for placement between adjacent vertebrae of claim 1wherein a spring located in said central axis is adapted to resilientlyflex perpendicularly to said central axis whereby said first plate andsaid second plate are dynamically associated.
 3. The spinal implant forplacement between adjacent vertebrae of claim 2 wherein said firstinterrupted skirt and said second interrupted skirt are concentric in aplane parallel with said first and second plates, said opposed arcs ofsaid first interrupted skirt are adapted to contact said opposed arcs ofsaid second interrupted skirt.
 4. The spinal implant for placementbetween adjacent vertebrae of claim 2 wherein said first plate includesa central bore, a sleeve secured in said bore, said depression formed insaid sleeve, said spring secured in said bore.
 5. The spinal implant forplacement between adjacent vertebrae of claim 2 wherein said opposedarcs of said first interrupted skirt and said opposed arcs of saidsecond interrupted skirt are concentric segments of a circle in a planeperpendicular to said first and second plates whereby said concentricsegments of said first interrupted skirt are adapted to contact saidconcentric segments of said second interrupted skirt to form aninterlocked universal joint.
 6. The spinal implant for placement betweenadjacent vertebrae of claim 1 wherein said first interrupted skirt andsaid second interrupted skirt are concentric in a plane parallel withsaid first and second plates, said opposed arcs of said firstinterrupted skirt are adapted to contact said opposed arcs of saidsecond interrupted skirt.
 7. The spinal implant for placement betweenadjacent vertebrae of claim 1 wherein said opposed arcs of said firstinterrupted skirt and said second interrupted skirt extend approximately90 degrees relative to each of said first interrupted skirt and saidsecond interrupted skirt, respectively.
 8. The spinal implant forplacement between adjacent vertebrae of claim 1 wherein said first plateincludes a central bore, a sleeve secured in said bore, said depressionformed in said sleeve.
 9. The spinal implant for placement betweenadjacent vertebrae of claim 1 wherein said opposed arcs of said firstinterrupted skirt and said opposed arcs of said second interrupted skirtare concentric segments of a circle in a plane perpendicular to saidfirst and second plates whereby said concentric segments of said firstinterrupted skirt are adapted to contact said concentric segments ofsaid second interrupted skirt to form an interlocked universal joint.10. The spinal implant for placement between adjacent vertebrae of claim1 wherein said first plate includes a cavity between said depression andsaid vertebrae side, an O-ring spring secured in said cavity, said balladapted to flex said O-ring spring resulting in resilient compression.11. The spinal implant for placement between adjacent vertebrae of claim10 wherein said second plate includes a cavity between said seconddepression and said vertebrae side, an 0-ring spring secured in saidcavity, said ball adapted to flex said 0-ring spring resulting inresilient compression.
 12. The spinal implant f or placement betweenadjacent vertebrae of claim 1 wherein said second plate includes acavity between said second depression and said vertebrae side, an O-ringspring secured in said cavity, said ball adapted to flex said 0-ringspring resulting in resilient compression.
 13. The spinal implant forplacement between adjacent vertebrae of claim 1 wherein a plurality offirst plates of different sizes, a plurality of balls of different sizesand a plurality of second plates of different sizes comprise a kitwhereby a proper sized spinal implant can be selected from said kit. 14.The spinal implant for placement between adjacent vertebrae of claim 1wherein an elastic membrane extends between said first plate and saidsecond plate about the periphery of said first plate and said secondplate.
 15. The spinal implant for placement between adjacent vertebraeof claim 14 wherein said elastic membrane is continuous and a viscouspolymeric composition is located within said membrane.
 16. A spinalimplant for placement between adjacent vertebrae for resilient axialsupport comprising a first plate and a second plate, said first platehaving a planar vertebrae engaging side and a disk side, a firstfastener on said planar side for engaging a vertebrae, a firstinterrupted skirt on said disk side extending approximately normal tosaid plate, said first interrupted skirt formed as opposing arcs, afirst centrally located bore in said first plate, a slidable sleeve insaid bore, a depression in said disk side of said insert centrallylocated between said opposing arcs, said second plate having a secondplanar vertebrae engaging side and a second disk side, a second fasteneron said second planar side for engaging a vertebrae, a secondinterrupted skirt on said second disk side extending approximatelynormal to said second plate, said second skirt formed as opposing arcs,a second centrally located bore in said second plate, a second sleeve insaid second bore, a second depression on said second disk side of saidsecond plate centrally located between said opposing arcs, a universallyrotatable ball captured in said depression and said, second depression,said ball, said depression and said second depression each forming abearing surface, a first cover plate mounted on said planar side of saidfirst plate closing said bore and secured to said first plate, an O-ringspring for resilient compression between said insert and said coverplate, a second cover plate mounted on said planar side of said secondplate closing said second bore and secured to said second plate, asecond O-ring spring for resilient compression between said secondinsert and said second cover plate, said first interrupted skirt andsaid second interrupted skirt being concentric in a plane parallel withsaid first and second plates, said opposed arcs of said firstinterrupted skirt contacting said opposed arcs of said secondinterrupted skirt, said opposed arcs of said first interrupted skirt andsaid opposed arcs of said second interrupted skirt being concentricsegments of a circle in a plane perpendicular to said first and secondplates whereby said concentric segments of said first interrupted skirtcontact said concentric segments of said second interrupted skirt toform an interlocked universal joint.
 17. A method of assembling aresilient spinal implant comprising the steps of: a) providing a firstplate, said first plate having a planar vertebrae engaging side and adisk side, a first interrupted skirt on said disk side extendingapproximately normal to said plate, said skirt formed as opposingseparated arcs, a depression in said disk side of said plate centrallylocated between said opposing arcs, b) providing a second plate having asecond planar vertebrae engaging side and a second disk side, a secondinterrupted skirt on said second disk side extending approximatelynormal to said second plate, said second skirt formed as opposingseparated arcs, a second depression in said second disk side of saidsecond plate centrally located between said opposing arcs, c) providinga ball and placing said ball in said depression, d) orienting said firstplate and said second plate parallel with each other with saidinterrupted skirt of said first plate located between said opposing arcsof said second plate, e) moving said interrupted skirt of said firstplate between said opposing arcs of said second plate to engage saidball into said depression and said second depression in axial alignment,and f) rotating said first plate with respect to said second plate abouta central axis until said interrupted skirt of said first plateinterlocks with said opposing arcs of said second plate.
 18. A method ofmanufacture of a spinal prosthesis comprising the steps of: a) forming aplate having a planar surface and a periphery in the general shape ofthe end wall of a vertebra; b) forming a central through bore in saidplate; c) forming a depending skirt on one side of said plate; d)forming an elongated sleeve having a depression in one end; e) insertingsaid sleeve in said through bore with said skirt being concentric withsaid depression; f) inserting a cover plate in said through bore andbonding said cover plate to said planar surface; g) forming a secondplate having a second planar surface and a second periphery in thegeneral shape of the end wall of a vertebra; h) forming a second centralbore in said second plate; i) forming a second depending skirt on oneside of said second plate between said second through bore and saidsecond periphery, said second depending skirt having a lesser diameterthan said depending skirt, said second depending skirt and saiddepending skirt being in contact with each other; j) forming a secondelongated sleeve having a second depression in one end; k) insertingsaid second sleeve in said second through bore with said second skirtbeing concentric with said depression; l) inserting a second cover platein said second through bore and bonding said second cover plate to saidsecond planar surface; and m) forming a ball of a size closelyapproximating the size of said depression and said second depression.19. The method of manufacture of a spinal prosthesis of claim 18comprising the steps of: a) forming a cavity on the other end of saidsleeve; and b) inserting an O-ring spring in said cavity whereby saidsleeve is resiliently movable relative to said plate.